The present invention relates to the field of plant molecular biology, more particularly to regulation of gene expression in plants.
Expression of heterologous DNA sequences in a plant host is dependent upon the presence of an operably linked promoter that is functional within the plant host. Choice of the promoter sequence will determine when and where within the organism the heterologous DNA sequence is expressed. Where expression in specific tissues or organs is desired, tissue-preferred promoters may be used. In contrast, where gene expression in response to a stimulus is desired, inducible promoters are the regulatory element of choice. Where continuous expression is desired throughout the cells of a plant, constitutive promoters are utilized. Additional regulatory sequences upstream and/or downstream from the core promoter sequence may be included in expression constructs of transformation vectors to bring about varying levels of expression of heterologous nucleotide sequences in a transgenic plant.
Frequently it is desirable to have constitutive or inducible expression of a DNA sequence throughout the cells of an organism in a tissue-independent manner. For example, increased resistance of a plant to infection by soil- and air-borne pathogens might be accomplished by genetic manipulation of the plant""s genome to comprise a constitutive promoter operably linked to a heterologous pathogen-resistance gene such that pathogen-resistance proteins are continuously expressed throughout the plant""s tissues.
Alternatively, it might be desirable to inhibit expression of a native DNA sequence within a plant""s tissues to achieve a desired phenotype. In this case, such inhibition might be accomplished with transformation of the plant to comprise a constitutive, tissue-independent promoter operably linked to an antisense nucleotide sequence, such that constitutive expression of the antisense sequence produces an RNA transcript that interferes with translation of the mRNA of the native DNA sequence.
Currently, only a few promoters that exhibit a constitutive pattern of expression in plants are available, examples of which include the CaMV 35S, nopaline synthase, and the ubiquitin promoters. The increasing interest in cotransforming plants with multiple plant transcription units (PTU) and the potential problems associated with using common regulatory sequences for these purposes merit having a number of such promoter sequences available.
Thus, isolation and characterization of constitutive promoters that can serve as regulatory regions for expression of heterologous nucleotide sequences of interest are needed for genetic manipulation of plants.
Compositions and methods for regulating expression of heterologous nucleotide sequences in a plant are provided. Compositions are novel nucleotide sequences for promoters that initiate transcription in a tissue-independent or constitutive manner, more particularly transcriptional initiation regions isolated from the plant genes Actin-2, Enolase, Gos-2 and L41. A method for expressing a heterologous nucleotide sequence in a plant using the transcriptional initiation sequences disclosed herein is provided. The method comprises transforming a plant cell with a transformation vector that comprises a heterologous nucleotide sequence operably linked to one of the plant promoters of the present invention and regenerating a stably transformed plant from the transformed plant cell. In this manner, the promoter sequences are usefuil for controlling the expression of operably linked coding sequences in a constitutive manner.
Downstream from and under the transcriptional initiation regulation of the promoter will be a sequence of interest that will provide for modification of the phenotype of the plant. Such modification includes modulating the production of an endogenous product, as to amount, relative distribution, or the like, or production of an exogenous expression product to provide for a novel function or product in the plant.